1. Field of the Invention
The present invention relates generally to the field of oxygen scavenging packaging articles. More particularly, it concerns oxygen scavenging packaging articles wherein oxygen scavenging is initiated by exposure of the packaging article to a peroxide and subsequently an initiating factor, such as heat or ultraviolet light.
2. Description of Related Art
It is well known that limiting the exposure of oxygen-sensitive products to oxygen maintains the quality and extends the shelf-life of the product. For instance, by limiting the oxygen exposure of oxygen sensitive food products in a packaging system, the quality of the food product is maintained, and food spoilage is avoided. Such packaging keeps the product in inventory longer, thereby reducing costs incurred from waste and restocking. In the food packaging industry, several means for limiting oxygen exposure have already been developed, including modified atmosphere packaging (MAP), vacuum packaging and oxygen barrier film packaging.
Another, more recent, means for limiting oxygen exposure involves incorporating an oxygen scavenger into the packaging structure. Incorporation of a scavenger in the package can scavenge oxygen present in the package upon filling with a product. In addition, such incorporation can provide a means of intercepting and scavenging oxygen as it passes through the walls of the package (herein referred to as an xe2x80x9cactive oxygen barrierxe2x80x9d), before the oxygen could reach the packaged product, thus providing even more protection to the packaged product.
In many cases, however, the onset of oxygen scavenging in this system may not occur for days or weeks. The delay before the onset of useful oxygen scavenging is hereinafter referred to as the induction period. Much work has been done to minimize the induction period. Primarily, this work has initiated oxygen scavenging by exposure of the oxygen scavenging packaging article to radiation, especially ultraviolet light (UV) radiation, although other actinic radiation or heat may also be used as an initiating factor.
Typically, the oxygen scavenging packaging article comprises a photoinitiator. Exposure of the packaging article to UV radiation activates the photoinitiator, which presumably depletes any antioxidant present in the packaging article or otherwise allows oxygen to irreversibly react with the oxygen scavenging material.
However, even with the use of a photoinitiator, the induction period is often longer than desired, due to the time required to build up a significant level of free radicals to effectively scavenge oxygen in the package.
Therefore, a need exists for reducing the induction period after triggering by UV, heat, actinic radiation, or another initiating factor or combination of factors.
In one embodiment, the present invention is directed to a method of initiating oxygen scavenging in a packaging article comprising an oxygen scavenging polymer, comprising (i) providing the packaging article comprising the oxygen scavenging polymer, wherein the packaging article comprises an interior surface and an exterior surface; (ii) wetting the interior surface of the packaging article with a solution comprising a peroxide, to result in a packaging article with a surface wetted with the peroxide; and (iii) exposing the surface wetted with the peroxide to an initiating factor, to initiate oxygen scavenging by the packaging article. Preferably, the initiating factor is ultraviolet light or heat. Also preferably, between wetting and exposing is performed a drying step, in which the solvent component of the solution is removed from the wetted surface.
The packaging article can also comprise additives known to be useful in oxygen scavenging packaging articles, such as a transition metal catalyst, a photoinitiator, an antioxidant, and structural polymers, among others. The packaging article can be a single-layer or multilayer packaging article, and the additional layers in the multilayer packaging article can comprise an oxygen barrier layer, an oxygen permeable layer, a structural layer, or an adhesive layer, among others.
The method has the advantages of being able to initiate oxygen scavenging by a packaging article comprising an oxygen scavenging polymer and a photoinitiator more rapidly than that initiated by methods previously known. In addition, the use of a peroxide solution and exposure to ultraviolet light or heat, or both, among other initiating factors, will also tend to sterilize the surface of the packaging article to which they are applied.